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Message-Id: <20201103182109.1014179-5-mic@digikod.net>
Date: Tue, 3 Nov 2020 19:21:01 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: James Morris <jmorris@...ei.org>,
"Serge E . Hallyn" <serge@...lyn.com>
Cc: Mickaël Salaün <mic@...ikod.net>,
Al Viro <viro@...iv.linux.org.uk>,
Andy Lutomirski <luto@...capital.net>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
Arnd Bergmann <arnd@...db.de>,
Casey Schaufler <casey@...aufler-ca.com>,
Jann Horn <jannh@...gle.com>, Jeff Dike <jdike@...toit.com>,
Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Richard Weinberger <richard@....at>,
Shuah Khan <shuah@...nel.org>,
Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org,
linux-security-module@...r.kernel.org, x86@...nel.org,
Mickaël Salaün <mic@...ux.microsoft.com>
Subject: [PATCH v23 04/12] landlock: Add ptrace restrictions
From: Mickaël Salaün <mic@...ux.microsoft.com>
Using ptrace(2) and related debug features on a target process can lead
to a privilege escalation. Indeed, ptrace(2) can be used by an attacker
to impersonate another task and to remain undetected while performing
malicious activities. Thanks to ptrace_may_access(), various part of
the kernel can check if a tracer is more privileged than a tracee.
A landlocked process has fewer privileges than a non-landlocked process
and must then be subject to additional restrictions when manipulating
processes. To be allowed to use ptrace(2) and related syscalls on a
target process, a landlocked process must have a subset of the target
process's rules (i.e. the tracee must be in a sub-domain of the tracer).
Cc: James Morris <jmorris@...ei.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Serge E. Hallyn <serge@...lyn.com>
Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
Reviewed-by: Jann Horn <jannh@...gle.com>
---
Changes since v21:
* Fix copyright dates.
Changes since v14:
* Constify variables.
Changes since v13:
* Make the ptrace restriction mandatory, like in the v10.
* Remove the eBPF dependency.
Previous changes:
https://lore.kernel.org/lkml/20191104172146.30797-5-mic@digikod.net/
---
security/landlock/Makefile | 2 +-
security/landlock/ptrace.c | 120 +++++++++++++++++++++++++++++++++++++
security/landlock/ptrace.h | 14 +++++
security/landlock/setup.c | 2 +
4 files changed, 137 insertions(+), 1 deletion(-)
create mode 100644 security/landlock/ptrace.c
create mode 100644 security/landlock/ptrace.h
diff --git a/security/landlock/Makefile b/security/landlock/Makefile
index 041ea242e627..f1d1eb72fa76 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -1,4 +1,4 @@
obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
landlock-y := setup.o object.o ruleset.o \
- cred.o
+ cred.o ptrace.o
diff --git a/security/landlock/ptrace.c b/security/landlock/ptrace.c
new file mode 100644
index 000000000000..77c77bb1fe97
--- /dev/null
+++ b/security/landlock/ptrace.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Ptrace hooks
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@...ikod.net>
+ * Copyright © 2019-2020 ANSSI
+ */
+
+#include <asm/current.h>
+#include <linux/cred.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/lsm_hooks.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+
+#include "common.h"
+#include "cred.h"
+#include "ptrace.h"
+#include "ruleset.h"
+#include "setup.h"
+
+/**
+ * domain_scope_le - Checks domain ordering for scoped ptrace
+ *
+ * @parent: Parent domain.
+ * @child: Potential child of @parent.
+ *
+ * Checks if the @parent domain is less or equal to (i.e. an ancestor, which
+ * means a subset of) the @child domain.
+ */
+static bool domain_scope_le(const struct landlock_ruleset *const parent,
+ const struct landlock_ruleset *const child)
+{
+ const struct landlock_hierarchy *walker;
+
+ if (!parent)
+ return true;
+ if (!child)
+ return false;
+ for (walker = child->hierarchy; walker; walker = walker->parent) {
+ if (walker == parent->hierarchy)
+ /* @parent is in the scoped hierarchy of @child. */
+ return true;
+ }
+ /* There is no relationship between @parent and @child. */
+ return false;
+}
+
+static bool task_is_scoped(const struct task_struct *const parent,
+ const struct task_struct *const child)
+{
+ bool is_scoped;
+ const struct landlock_ruleset *dom_parent, *dom_child;
+
+ rcu_read_lock();
+ dom_parent = landlock_get_task_domain(parent);
+ dom_child = landlock_get_task_domain(child);
+ is_scoped = domain_scope_le(dom_parent, dom_child);
+ rcu_read_unlock();
+ return is_scoped;
+}
+
+static int task_ptrace(const struct task_struct *const parent,
+ const struct task_struct *const child)
+{
+ /* Quick return for non-landlocked tasks. */
+ if (!landlocked(parent))
+ return 0;
+ if (task_is_scoped(parent, child))
+ return 0;
+ return -EPERM;
+}
+
+/**
+ * hook_ptrace_access_check - Determines whether the current process may access
+ * another
+ *
+ * @child: Process to be accessed.
+ * @mode: Mode of attachment.
+ *
+ * If the current task has Landlock rules, then the child must have at least
+ * the same rules. Else denied.
+ *
+ * Determines whether a process may access another, returning 0 if permission
+ * granted, -errno if denied.
+ */
+static int hook_ptrace_access_check(struct task_struct *const child,
+ const unsigned int mode)
+{
+ return task_ptrace(current, child);
+}
+
+/**
+ * hook_ptrace_traceme - Determines whether another process may trace the
+ * current one
+ *
+ * @parent: Task proposed to be the tracer.
+ *
+ * If the parent has Landlock rules, then the current task must have the same
+ * or more rules. Else denied.
+ *
+ * Determines whether the nominated task is permitted to trace the current
+ * process, returning 0 if permission is granted, -errno if denied.
+ */
+static int hook_ptrace_traceme(struct task_struct *const parent)
+{
+ return task_ptrace(parent, current);
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+ LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
+ LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
+};
+
+__init void landlock_add_hooks_ptrace(void)
+{
+ security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+ LANDLOCK_NAME);
+}
diff --git a/security/landlock/ptrace.h b/security/landlock/ptrace.h
new file mode 100644
index 000000000000..6740c6a723de
--- /dev/null
+++ b/security/landlock/ptrace.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Ptrace hooks
+ *
+ * Copyright © 2017-2019 Mickaël Salaün <mic@...ikod.net>
+ * Copyright © 2019 ANSSI
+ */
+
+#ifndef _SECURITY_LANDLOCK_PTRACE_H
+#define _SECURITY_LANDLOCK_PTRACE_H
+
+__init void landlock_add_hooks_ptrace(void);
+
+#endif /* _SECURITY_LANDLOCK_PTRACE_H */
diff --git a/security/landlock/setup.c b/security/landlock/setup.c
index 39ee1766f175..5e7540fdeefa 100644
--- a/security/landlock/setup.c
+++ b/security/landlock/setup.c
@@ -11,6 +11,7 @@
#include "common.h"
#include "cred.h"
+#include "ptrace.h"
#include "setup.h"
struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = {
@@ -20,6 +21,7 @@ struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = {
static int __init landlock_init(void)
{
landlock_add_hooks_cred();
+ landlock_add_hooks_ptrace();
pr_info("Up and running.\n");
return 0;
}
--
2.28.0
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